This invention relates generally to pixel sensors. More particularly, this invention relates a self-aligned metal electrode structure for elevated sensors.
An array of image sensors or light sensitive sensors detect the intensity of light received by the image sensors. The image sensors typically generate electrical signals that have amplitudes that are proportionate to the intensity of the light received by the image sensors. The image sensors can convert an optical image into a set of electronic signals. The electronic signals may represent intensities of colors of light received by the image sensors. The electronic signals can be conditioned and sampled to allow image processing.
Integration of the image sensors with signal processing circuitry is becoming more important because integration enables miniaturization and simplification of imaging systems. Integration of image sensors along with analog and digital signal processing circuitry allows electronic imaging systems to be low cost, compact and require low power consumption.
FIG. 1 shows a portion of a prior art integrated circuit image sensor array. The integrated circuit image sensor array includes a substrate 100. An interconnection structure 120 is formed adjacent to the substrate 100. Pixel metallization layers 130 and doped layers 140 form individual sensor electrodes. The sensor electrodes are electrically connected to the substrate 100 through conductive vias 125 within the interconnection structure 120. The sensors can further include an I-layer 150, an outer electrode layer 160 and a conductive layer 170. Generally, the sensor electrodes form cathodes of the image sensors. The transparent conductor 170 provides biasing of the anodes of the image sensors.
Typically, the interconnection structure 120 is a standard CMOS interconnection structure. The interconnection structure 120 includes the conductive vias 125 which provide electrical connections between the substrate 100 and the sensor electrodes.
The pixel metallization layers 130 should include a thin conductive material. The pixel metallization layers 130 are be optional. However, the pixel metallization layers 130 have a lower resistance than the materials used to form the doped layers 140. Therefore, the pixel metallization layers 130 provide better current collection.
The doped layers 140 are generally formed from a doped semiconductor. The doped semiconductor can be an N-layer of amorphous silicon. The doped layers 140 must be thick enough, and doped heavily enough that the doped layers 140 do not fully deplete when the sensors are biased during operation.
Methods of forming the pixel electrode structure shown in FIG. 1 require two material deposition steps and two material removal steps. That is, the methods require a step for depositing a pixel metallization layer, a step for selectively removing portions of the pixel metallization layer, a step for depositing a doped layer, and a step for selectively removing portions of the doped layer. The two material removal steps require lithographically forming masks according to predetermined patterns. That is, a mask must be lithographically formed before removing a predetermined pattern of the pixel metallization layer, and a mask must be lithographically formed before removing a predetermined pattern of the doped layer.
It is desirable to have a simplified metal sensor electrode structure which requires fewer processing steps to form than present metal sensor electrode structures.
The present invention is a self-aligned metal electrode structure for elevated sensors. Formation of the self-aligned metal electrode structure requires fewer processing steps than presently existing sensor structures.
A first embodiment of the invention includes a self-aligned metal electrode sensor structure. The self-aligned metal electrode sensor structure includes a substrate which includes electronic circuitry. An interconnect structure is formed adjacent to the substrate. The interconnect structure includes conductive interconnect vias which pass through the interconnect structure. A sensor is formed adjacent to the interconnect structure. The sensor includes a pixel metallization section and a doped layer electrode. The pixel metallization section is electrically connected to the interconnect via. The pixel metallization section includes an outer surface which is substantially planar. The doped layer electrode includes an inner surface adjacent to the outer surface of the pixel metallization section. The entire inner surface of the doped layer electrode is substantially planar. A transparent conductive layer is formed adjacent to the sensor. The interconnect via and the transparent conductive layer electrically connect the electronic circuitry to the sensor.
A second embodiment of the invention is similar to the first embodiment. The second embodiment includes the outer surface of the pixel metallization section having an outer surface area which is substantially equal to an inner surface area of the inner surface of the doped layer electrode.
A third embodiment of the invention is similar to the first embodiment. The third embodiment includes the outer surface of the pixel metallization section having an outer surface area which is less than an inner surface area of the inner surface of the doped layer electrode.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.